_________________________________________________________________________________________ It is the primary objective of this program to elucidate correlates of immune-mediated protection against HIV-1 infection using pre-clinical animal models. To this end, Project 1 will determine humoral and cell-mediated immune responses to an attenuated SIV, termed SIVGY that induces protective immunity to subsequent challenge with a heterologous pathogenic SIV. Project 3 will determine immune responses elicited by different prime-boost vaccine regimens using combinations of DNA vaccines, E1-deleted adenovirus (Ad) vectors and poxvirus vectors. Project 2 will use passive immunization with neutralizing antibodies to determine baseline parameters of antibody-mediated protection with the long-term to develop vaccines that induce B and T cells. Project 3 will assess the role of vaccine-induced mucosal T cells in limiting the spread of SIV. It is the secondary objective of this program to determine if vaccine-induced immune responses including those induced by Ad vectors can be detrimental and if further modifications of E1-deleted Ad vectors can improve both their safety and immunogenicity/efficacy. To this end, Project 3 will test the hypothesis that CD4+ T cell responses induced by viral vector vaccines against the transgene product or components of the vector facilitate disease progression upon SIV infection of nonhuman primates. Project 1 will attempt to improve the efficacy and safety profile of Ad vector vaccines by generating and testing 2nd generation E1-deleted Ad vectors that will have an additional deletion of E2a to reduce synthesis of the highly immunogenic structural antigens of Ad vectors. The application is subdivided into the following 3 Projects and 2 Cores. Project 1 (H. Ertl): Vaccine-Induced Correlates of Protection Project 2 (R. Ruprecht): Neutralizing Antibody Coverage for CTL Vaccines Project 3 (G. Silvestri): Mucosal T Cell Responses and Protection from Simian AIDS Core A (H. Ertl): Administrative Core Core B (X. Zhou): Vector Core